1. Field of the Invention
The present invention relates a tuner apparatus for receiving TV broadcasting.
2. Description of Related Invention
A typical currently used tuner unit is configured, for example, as shown in FIG. 1. Terrestrial TV broadcasting waves are received by an antenna 11 and the received broadcast wave signals SRX pass through an input bandpass filter 12, a radio frequency amplifier 13, and a bandpass filter 14, which form a signal line, and are supplied to a mixer circuit 15.
To the mixer circuit 15, oscillation signals in a predetermined frequency band are supplied from an oscillator circuit 16. In the mixer, by using the oscillation signals, the target channel broadcast wave signals out of the broadcast wave signals SRX are frequency-converted into intermediate-frequency signals SIF. These SIF signals, after passing through an intermediate-frequency amplifier 17, are outputted at a terminal 18 and subjected to further processing.
The same tuner configuration and operation are also true for CATV broadcasting, except that broadcast waves are inputted by means of a coaxial cable instead of the antenna
On the other hand, a tuner unit for satellite digital TV broadcasting is configured, for example, as shown in FIG. 2. This tuner is a double-superheterodyne type. Broadcast waves from a satellite are received by a parabolic antenna unit 21 and frequency-converted into first intermediate-frequency signals SIF1 in a predetermined intermediate frequency band. The SIF1 signals pass through a first intermediate-frequency filter 22, a first intermediate-frequency amplifier 23, and a first intermediate-frequency filter 24, which form a signal line, and are supplied to a mixer circuit 25.
To the mixer circuit 25, oscillation signals in a predetermined frequency band are supplied from an oscillator circuit 26. In the mixer, by using the oscillation signals, the first intermediate-frequency signals as target channel broadcast wave signals out of the SIF1 signals are frequency-converted into second intermediate-frequency signals SIF2. The SIF2 signals, after passing through a second intermediate-frequency filter 27 and a second intermediate-frequency amplifier 28, are supplied to a quadrature detector circuit 31.
To the detector circuit 31, oscillation signals for quadrature detection in a frequency band identical to the second intermediate-frequency band, but with the phase being shifted 90 degrees from the phase of the second intermediate-frequency signals, are supplied from an oscillator circuit 32. In the detector circuit 31, by using the oscillation signals, the second intermediate-frequency signals are demodulated into baseband signals SI and SQ that correspond to their in-phase component and quadrature component (real axis component and imaginary axis component). These SI and SQ signals are outputted at terminals 331 and 33Q and subjected to further processing.
Another type of tuner unit for satellite digital TV broadcasting is, for example, as shown in FIG. 3. Broadcast waves from a satellite are received by a parabolic antenna unit 21 and frequency-converted into first intermediate-frequency signals SIF1 in a predetermined intermediate-frequency band. The first SIF1 signals pass through a first intermediate-frequency filter 22, a first intermediate-frequency amplifier 23, and a first intermediate-frequency filter 24, which form a signal line, and are supplied to a quadrature detector circuit 31.
To the detector circuit 31, oscillation signals for quadrature detection in a frequency band identical to the frequency band of the first intermediate-frequency signals as target channel signals out of the SIF1 signals, but with the phase being shifted 90 degrees from the phase of the first intermediate-frequency signals are supplied from an oscillator circuit 32. In the detector circuit, by using the oscillation signals, the SIF1 signals are demodulated into baseband signals SI and SQ which correspond to their in-phase component and quadrature component (real axis component and imaginary axis component). These SI and SQ signals are outputted at terminals 331 and 33Q and subjected to further processing.
The broadcast wave-receiving tuner shown in FIG. 3 is called a direct conversion type or alternatively a zero IF circuit type because the second intermediate frequency is 0. The circuit configuration of this tune unit is simpler than that of the double-superheterodyne tuner shown in FIG. 2.
Meanwhile, recently, an increasing number of people wish to have a single receiver capable of receiving terrestrial TV broadcasting, CATV broadcasting, and satellite digital TV broadcasting.
If a single receiver is configured so as to be capable of receiving these three types of TV broadcasting, the tuner unit shown in FIG. 1 and the tuner unit shown in FIG. 2 or FIG. 3 must be integrated into the single receiver. This, however, poses some problem such as increase of the cost of producing the receiver and enlargement of the receiver.